Every form of classical vaccine, namely the use of killed virus, live attenuated virus, and various combinations of subunits of virus, has been tried for the prevention of HIV infection, to no good effect. It had been found that the classical vaccines worked as intended, but that the resulting immune response, an antibody response, was fundamentally unable to inhibit infection in animal models.
The present inventors have shown that, if an antigen is taken up by immune system cells and expressed in the lymphoid organs, different immune responses can be raised, and might have the potential to control the virus. See U.S. Ser. No. 08/803,484 “Methods and Compositions for Therapeutic and Genetic Immunization, filed Feb. 20, 1997 by J. Lisziewicz and F. Lori. The text of that application is incorporated by reference herein as if set forth in full. That application further disclosed that, while any number of antigens, including viral particles, might be used to raise the immune responses, it would be preferable to use a replication-defective virus due to safety considerations. The application explains that replication-defective viral particles themselves have been shown to be ineffective for raising immune responses. Rather than use viral particles, the inventors preferred to use a different material, a plasmid DNA encoding a replication-defective virus. The application discloses various types of replication-defective viruses to select for encoding, and suggests various ways to obtain replication-defective retroviruses, in particular by alteration of the integrase and gag genes. The inventors have demonstrated that a plasmid DNA encoding a replication-defective virus can be made used to induce immune responses, and that furthermore, such materials can be administered topically without the use of needles See U.S. Pat. No. 6,420,176, Method of Delivering Genes into Antigen Presenting Cells, issued Jul. 16, 2002 to Lisziewicz and Lori. The text of this patent is incorporated herein as if set forth in full.
The inventors have also demonstrated that plasmid DNA encoding a replication-defective virus having an altered integrase gene can be used in conjunction with an effective antiviral drug regimen to treat an existing infection. In a situation where antiviral drugs are able to control an infection but not eradicate it, the drugs can be used until the virus replication is controlled, and then the patient can be treated with the plasmid DNA composition. After this therapeutic vaccine treatment, the patient may exhibit enhanced immune system function, and decreased need for drug treatment. (See U.S. Ser. No. 09/863,606 “Therapeutic DNA vaccination,” filed May 23, 2001 by Lisziewicz and Lori,). The examples of that application use an experimental plasmid DNA that was not intended for use in humans.
The inventors now describe a new plasmid DNA for the induction of T cell-mediated immune responses, which can be used to make improved DNA formulations. The plasmid DNA comprises one or more DNA sequences encoding antigenic materials operably linked to a promoter and also having a truncated 3′ LTR. The promoter is preferably a 5′ LTR. The truncated 3′ LTR is important because this feature alone renders any retrovirus encoded by the DNA replication-defective. These DNA can be administered to mammals by any of the previously described methods. However, the inventors prefer topical administration, as this method is both efficient and comfortable for the patient.
Plasmid DNA has been used by both the present inventors and others for induction of immune responses against different pathogens, including HIV. For example, U.S. Pat. No. 6,214,804 describes the use of a different DNA composition, specifically a DNA encoding the protein gp120 operably linked to a CMV promoter. As discussed herein, a CMV promoter is a constitutive promoter, which is less efficient than an inducible promoter. Further, there is no disclosure or discussion of the use of a truncated 3′ LTR, or the advantages that may be obtained by its use.
In another example, WO 99/43350 (PCT/US99/04128) describes the use of ADP-ribosylating exotoxins as vaccine adjuvants. An advantage of the present invention is that the formulation can be fully comprised of materials having very low toxicity. In yet another example, U.S. Pat. No. 6,348,450 B1 describes the use of adenovirus vectors as adjuvants in combination with DNA vaccines. The reference discloses that such vectors are immunogenic, and are of limited utility where the target individual has already been exposed to such vectors. An advantage of the present invention is that it need not rely on the use of any immunogenic adjuvants. Therefore, unwanted immunogenic responses are minimized.
Other references disclose the use of DNA vaccines in animals. In particular, primate animal models are widely used for studies involving new preventive and therapeutic approaches for HIV infection (Robinson, H. L. (2002). “New hope for an AIDS vaccine.” Nature Rev Immunol 2(4): 239–50.). In this reference some of the DNA vaccines administered in combination with other vaccines prior to infection have demonstrated inhibition of viral replication after challenge (Robinson 2002). All of the previously described DNA vaccine constructs had a sequence composition of expressing one or more HIV genes operably linked to CMV promoter. None of these constructs were operably linked to an HIV 5′ LTR promoter and none of these constructs were operably linked to a truncated 3′ LTR. In our previous applications (PCT US97/02933) we have described a novel composition of DNA vaccine that expresses of replication defective viruses that expresses viral genes operably linked to 5′ LTR promoter. In this application we further specify the composition of the DNA by operably linking one or more genes to the truncated 3′ LTR and a promoter.